The Pedroza Thumbnail extension does not add WRITE_EXTERNAL_STORAGE to the Manifest. Therefore the app can’t ask for it. Permissions MUST be declared in the Manifest to ask for them.
So try to add the File component (as a dummy, without using it) to your app. Build the APK and try again.
Note: There is no need to use special blocks anymore (→ Daily Challange 46), so remove them.